Make a quick pass on analyzer performance

[Youssef1313]

As we keep adding more and more analyzers, I would like us to make sure they are written in a performant way and that we are not slowing down the build for test projects.

I'm not suspecting any specific perf issues for any specific analyzers. This issue is just to validate that our perf is good. The performance of MSTest/MTP at runtime is equally important to performance of build :)